An accurate mechanism for delivering precise drug dose of aerosol drugs into the interior of human beings has been an objective of many workers in the art. One of the most popular aerosol delivery devices is the propellant driven metered dose inhaler (MDI) which releases metered dose of medicine upon each actuation.
U.S. Pat. No. 5,364,838 discloses an intrapulmonary device for administering insulin which contains a system for determining inspirational air flow created by a patient inhaling through the mouthpiece which has a microprocessor that collects data from an airflow detector.
U.S. Pat. No. 5,458,135 discloses a device for administering doses of powder aerosol drugs which contains a microprocessor and a key pad for inputting information to the microprocessor. The device contains a dosage recall button, a LCD which displays dates, times, puffs and dosage history.
None of the prior art devices provide a means for controlling the flow rate so that the inhaled medicament would be within a selected amount to avoid over dosing and/or under dosing.
When the inhalation devices are used by children or invalids, the accuracy of reported doses and/or amount of drug used in the treatment of a pulmonary disease can be questionable. An overdose or an underdose can cause a problem to the patient who is relying upon an accuracy of dosage. A need to know dosage and amount of administered drug is important in preventing underdosing or overdosing.
It is desirable that the patient be able to know if the dose is within the required range. Furthermore, it has been shown that few patients are able to tell when a correct dosage has been administered or if they are properly using the inhalation device.
Workers in the art have attempted to provide a metered dose of a medicant by using dry powder inhalers (DPI). Such devices normally rely on a burst of inspired air that is drawn through the unit. However, these units are disadvantaged in that the force of inspiration varies considerably from person to person. Some patients are unable to generate sufficient flow to activate the unit.
Other workers in the art have refined aqueous nebulization delivery systems. Although such systems require a continuous gas compressor, making them less portable than the MDI's and the DPI's, many nebulizers provide a low velocity aerosol which can be slowly and deeply inhaled into the lungs. Precision of dosage delivery, however, remains a serious problem and it is difficult to determine how much medicament the patient has received. Most nebulizers operate continuously during inhalation and exhalation. Dosage is dependent on the number and duration of each breath. In addition to breath frequency and duration, the flow rate, i.e., the strength of the breath that is taken from a nebulizer can effect the particle size of the dose inhaled. The patient's inhalation acts as a vacuum pump that reduces the pressure in the nebulizer. A strong breath can draw larger unwanted particles of medicant out of the nebulizer. A weak breath, on the other hand, will draw insufficient medicament from the nebulizer.